A monoclonal antibody which recognizes the rat NGF receptor (MAB 192) has been shown following intraventricular injection to be internalized and transported specifically and bilaterally to most of the neurons of the cholinergic basal forebrain (CBF). The functional properties of the CBF are not well understood, partly because it is a diffuse system which has not, until now, been amenable to specific experimental manipulation, but it is implicated in learning, memory, and the regulation of sleep patterns. the CBF is one of the major sites of neuronal degeneration, and loss of cholinergic markers is one of the most consistent and severe neurochemical deficits in Alzheimer's disease (AD). The major goal of this proposal is to create an animal model of forebrain cholinergic deficit by the intraventricular delivery to the CBF of MAB 192 linked to a ribosome inactivating protein, saporin; this immunotoxin (IT) offers potentially superior specificity when compared with classical lesioning techniques. This toxin has been synthesized and delivered intraventricularly and in preliminary experiments shows clear evidence of major toxicity to NGF receptor-bearing cholinergic neurons; adjacent (and distant) non-NGF receptor-bearing, cholinergic neurons are unaffected. The animal model will be evaluated by morphological, biochemical, and behavioral techniques. The following is proposed toward the goal of using an IT to create a rat model of forebrain cholinergic deficit: 1) Preparing the IT's in sufficient quantities to use in vivo and establishing the dose and mode of intraventricular injection which will optimize the production of a forebrain cholinergic deficit, as judged by morphological and biochemical criteria. This will include studies designed to show whether actual neuron death, as opposed to loss of cholinergic phenotype, is produced by the IT; 2) Examining other brain regions [both non-cholinergic but NGF receptor (+) areas, cholinergic regions which are NGF receptor (-), and an unrelated system, that of the n. locus ceruleus] using similar methods to assess the specificity of the damage produced by the IT; 3) Evaluating behavioral deficits in learning, memory, and sleep patterns in rats with a well- characterized, IT-induced forebrain cholinergic deficit. This animal model will ultimately allow the investigation of the function of the CBF by examining the deficits (morphological, biochemical, behavioral) created by deletion of the system; the potential contribution of cholinergic deficits to the observed derangements in AD can also be assessed.